I employed the Montessori approach of teaching my preschoolers odd and even numbers. I’ve used what’s available in the box, our diy number cards from our teen board and counters which I have purchased before for 4 dirhams. Before teaching odd & even numbers a child should know at least numbers 1-10.
This is how we did it. I asked them to set up the number cards and place the corresponding counters. When all the counters were laid out, I point to single counter, which is numeral 1 and point out its and “odd”. Then I point to the numeral 2 which has a pair of counters and say this is “even”. Continue the process to 10. Help the child understand that “even” is pair while “odd” is not. Then ask them to show you which is odd or even.
This is an easy and concrete way of teaching them this lesson. If you need more infos, google the lesson and you will find bunch of tutorials on how to present this to children.